Codable in Swift4

Codable_CodingKeys.swift

// When property name and key are different 

let data = """
{
"user_id":0,
"user_name": "name",
"mail-address": "address"
}
""".data(using: .utf8)!

struct User: Codable {
	let id: Int
	let name: String
	let address: String
	
	enum CodingKeys: String, CodingKey {
			case id = "user_id"
			case name = "user_name"
			case address = "mail-address"
	}
}

Codable_Error_KeyNotFound.swift

// Key not found property name
struct User: Codable {
	let id: Int
}

let data = "{"user_id":0}".data(using: .utf8)!

do {
	let user = try JSONDecoder().decode(User.self, from: data)
} catch let error {
	print(error) // keyNotFound
}

// Success
// property type change to Optional type
struct User: Codable {
	let id: Int?
}

let data = "{"user_id":0}".data(using: .utf8)!

do {
	let user = try JSONDecoder().decode(User.self, from: data)
} catch let error {
	print(error)
}

Codable_Error_TypeMismatch.swift

// property type and type of value are different
struct User: Codable {
	let id: Int
}

let data = "{"id":"id"}".data(using: .utf8)!

do {
	let user = try JSONDecoder().decode(User.self, from: data)
} catch let error {
	print(error) // typeMismatch
}

Codable_Usage.swift

struct User: Codable {
	let id: Int
	let name: String
	let address: String
}

let data = """
{
"id":0,
"name": "name",
"address": "address"
}
""".data(using: .utf8)!

// Decode
do {
	let user = try JSONDecoder().decode(User.self, from: data)
} catch  { }

// encode
do {
	let user = try JSONDecoder().decode(User.self, from: data)
	let data = try JSONEncoder().encode(user)
	let json = String(data: data, encoding: .utf8)!
} catch  { }

Dictionary_Struct.swift

protocol Dictionaryable: Codable {
	func encode() -> [String: Any]?
	static func decode(dictionary:[String: Any]) -> Self?
}

extension Dictionaryable {
	func encode() -> [String: Any]? {
		do {
			let data = try JSONEncoder().encode(self)
			return try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any]
		} catch let error {
			print(error)
			return nil
		}
	}
	
	static func decode(dictionary:[String: Any]) -> Self? {
		do {
			let data = try JSONSerialization.data(withJSONObject: dictionary, options: [])
			return try JSONDecoder().decode(Self.self, from: data)
		} catch let error {
			print(error)
			return nil
		}
	}
}

// Usage
struct User: Dictionaryable {
	let id: Int
	let name: String
	let address: String
}

let dictionary: [String: Any] = ["id": 0, "name": "name", "address": "address"]
let user = User.decode(dictionary: dictionary)

let user_ = User(id: 0, name: "name", address: "address")
let dictionary_ = user_.encode()

Save_UserDefaults.swift

protocol Saveable: Codable {
	func save(key: String)
	static func load(key: String) -> Self?
}

extension Saveable {
	func save(key: String) {
		do {
			let data = try JSONEncoder().encode(self)
			UserDefaults.standard.set(data, forKey: key)
		} catch let error {
			print(error)
		}
	}
	
	static func load(key: String) -> Self? {
		guard let data = UserDefaults.standard.data(forKey: key) else {
			return nil
		}
		
		do {
			return try JSONDecoder().decode(Self.self, from: data)
		} catch let error {
			print(error)
			return nil
		}
	}
}

// Usage
struct User: Saveable {
	let id: Int
	let name: String
	let address: String
}

let key = "user"
let user = User(id: 0, name: "name", address: "address")

user.save(key: key)
let user_ = User.load(key: key)